At least 1,400 passengers were affected at Warsaw's Frederic Chopin Airport. Some were transferred to other airlines.

The airline said in a statement on its website that the "IT attack" meant it was unable to create flight plans and flights were not able to depart from Warsaw.

The systems on the planes were safe and those with planned routes were able to return to the Polish capital, according to LOT's website.

LOT stressed that the glitch did not affect the airport or aeroplanes that were already in the air, said the BBC.

"We are secure," Mr Kubicki said. "We know the mechanism and if it was to happen again we're ready to react quickly."

Poland's Internal Security Agency is investigating the attack but it has made no comment. LOT said it has informed the police about the attack and is awaiting results of their investigation.

Concerns over aviation and hacking are on the rise, compounded by a new wave of airliners connected to the Internet, prompting fears that cyber terrorists could take control of planes remotely.

In December last year, the International Civil Aviation Organisation said cyber crime was a serious threat to safety in the skies, vowing to set up a "security culture" protecting travellers against any catastrophic incident.

A US report in April warned that hackers could exploit in-flight entertainment systems to fatally sabotage cockpit electronics.

The report by an investigative arm of the US Congress came just weeks after a co-pilot crashed his Germanwings A-320 plane into the French Alps, killing all 150 on board, and prompting talk of airliners one day being 100 per cent automated.

Last month, a security researcher claimed he had hacked the controls of a United Airlines jetliner from its entertainment system. The Federal Bureau of Investigation is investigating the claim by Mr Chris Roberts of One World Labs that he briefly took control of a United aircraft from his passenger seat by hacking into the in-flight entertainment network.

United cast doubt on the claims, with its CEO telling a US Senate hearing that there were "clear firewalls" between the systems, but admitting that the matter was "of great concern to us" and that the airline was cooperating with the FBI investigation.

AGENCE FRANCE-PRESSE, BLOOMBERG

A version of this article appeared in the print edition of The Straits Times on June 23, 2015, with the headline 'Flights restored after cyber attack: LOT Airlines'. Print Edition | Subscribe

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